Method of and apparatus for making heat exchanging elements



April 25, 1939. I A. J. ERG ET AL 2,155,394

METHOD OF AND APPARATUS FOR MAKING HEAT EXCHANGING ELEMENTS 3Sheets-Sheet l Filed Feb. 14, 1936 INVENTOR.

J 55/? Jon/1v Q1/0515 BY ATTORNEYS.

April 25, 19 39. A. J. BERG ET AL 2,155,394

METHOD GI 5N3 APPARATUS FOR MAKING HEAT EXCHANGINQ T LSMENTS Filed Feb.14, 1936 3 Sheets-Sheet 2 I ll! 2; 155,394 METHOD OF AND APPARATUS FORMAKING HEAT EXCHANGING ELEMENTS April 25,1939.

A. J. BERG ET AL Filed Feb. 14, 1,936 3 Sheets-Sheet 5 INVENTOR. fluke-0J 621% Jo/m' O. l/(ASE- ATTORNEYS.

Patented Apr. 25, 1939 METHOD OF AND APPARATUS FOR MAKING HEATEXCHANGING ELEMENTS Alfred J. Berg, Portsmouth, N. H., and John 0. Huse,United States Navy Application February 14, 1935, Serial No. 63,895

7 Claims. (01. 29-1573) (Granted under the act of March 3, 1883, asamended April 30, 1928; 370 0. G. 757) Our invention relates to a newand useful method of and apparatus for making heat or cold exchangingelements.

The objects of our invention are to provide a new and useful method ofand apparatus for making heat or cold exchanging elements which willenable the production of such elements more rapidly and cheaply, of,very high capacity for exchanging heat or cold, and which producedelements will be very light, strong and long enduring under theconditions encountered in use.

Other objects and advantages of our invention will be readily understoodby those skilled in this art from the following specification.

In the drawings, Figure 1 is a side elevation view partially incross-section of a heat or cold exchanging element illustrating typicalsteps in the transition of the product from its commencement until it isfinished; the left end illustrating the commencement, and theextremeright end illustrating the finish;

Fig.2 is a left end view of the parts shown in Fig. 1;

Fig. 3 is a view similar to Fig. 1 but including 5 the apparatusarranged to produce the requisite transitions from the commencement tothe completion of the finished product in accordance with our invention;

Fig. 4 is a right end elevation view of the parts 30 shown in Fig. 3;

Fig. 5 is a left side view of a single typical one of the rows ofbending and stretching tools, shown in Figs. 3 and 4;

Fig. 6 illustrates a detail of construction hereinafter described; and

Fig. 7 illustrates diagrammatically the front elevation view of a latheor similar tool which may be employed in the practice of our methodwhich may with substantially equal advantage be 40 practiced by a numberof different kinds of machines than herein indicated as will beunderstood by those skilled in this art.

In the drawings, in which like characters of reference indicate the samepart, It! represents 45 the body portion of the heat or cold exchangingelement which may be a tube or other shaped hollow body.

Heretofore, the heat or cold exchanging ribs or fins have'been disposededgewise upon the 50 body portion of the element with the rib or finthroughout the operation, regardless of whether the rib or fin belongitudinal, or formed in a ring, or wound helically, invariablymaintained with one edge in contact with the surface of the 5;; elementand the width of the rib or fin extending substantially at a right anglefrom the body of the element. In winding or ceiling the rib or finedgewise about the body of the element and maintaining the rib or finfree from wrinkles and other objectionable surface irregularities 5substantial lateral stress is required to be borne by the body portionof the element. This lateral stress was occasioned by longitudinalstress upon the straight portion Lu. the rib or fin as it was beingadvanced toward the stage of its edgewise 10 bending-or coiling aboutthe body of the element, as well as further occasioned by the lateralstresses occasioned by the means for maintaining the ribs or fins at aright angle to the tube or body portion of the element. Despite theprior 5 teachings of the art to wind the fin edgewise about the bodyportion of the element our present invention, in its method aspectindicated in .Figs. 1 and 2 commences to wind or coil, helically orotherwise, the strip ll about with one of its 20 broad sides toward, thetube or body portion ID of the heat or cold exchanging element. A broadthin fiat ribbon of metal II is loosely advanced toward body portion l0,not under longitudinal or other stress, with one of its broad lateralfaces substantially parallel with the outer surface of the tube or bodyportion l0. An end of said ribbon II is arranged in tangential contactwith a surface of the tube or body portion III, and, for instance, anarrow strip [2 at its left corner is secured to the tube'or bodyportion III by solder or otherwise. Progressively with the coiling ofsaid ribbon ll about the surface of tube or body portion III, a verynarrow strip I! of said ribbon H is progressively secured to said tubeor body 36 portion it). As the ribbon II is progressively coiled aroundor helically about the tube or body portion I0, free from longitudinalstress, the unsecured side of a previously bent or coiled portion ofribbon II is simultaneously bent and 40 stretched outwardly byprogressive degrees until the main body of the rib or fin is formed atsubstantially right angles to its foot l2 which remains secured to thesurface of the tube or body portion Ill. The initial fiat straightribbon H, as it a'pproaches the tube or body portion [0, is

in an unstressed condition which unstressed condition substantiallycontinues in its portion bent about the tube or body portion I0 untilthe same commences to be bent, arched and stretched outwardly, Saidoutward bending, arching and stretching produces a very substantiallongitudinal stress upon only the outwardly bent and stretched portionof the ribbon H. However, such longitudinalstress tends to produce nosub- 86 stantial lateral thrust upon the tube or body portion III forthe reason that such stress is unidirectional about the tube or bodyportion III. Such longitudinal stress of the portion, other than thesecured portion. I2, of the ribbon II, increases somewhat with thedegree of outward bending or forming and stretching to which the same isprogressively subjected until the main body of the ribbon II projects atsubstantially a right angle from the tube or body portion III, in whichlatter position the right angle portion of the ribbon II, which is ofits normal thickness at its juncture with its foot I2, becomesprogressively thinner as it extends beyond its foot I2. In this rightangled or finished position of the main .width portion of ribbon II somelongitudinal stress is maintained in the rib or fin so formed from thefiat unstressed ribbon II. Such longitudinal stress is so maintained bythe foot I2 as well as by its securement at progressive intervals orcontinuously to the wall of tube or body portion ID. This longitudinalstress maintained in the finished rib or fin enables a very much thinnerand wider ribbon II of metal to be employed in the production of the ribor fin, because the same maintains such thinner formed rib or fin in itsinitially fixed position by said longitudinalstress substantiallyincreasing its resistance to deformation and distortion, accidentalmetal along one edge of ribbon II, which'strip forms the foot I2.

The various progressive transition stages of the foregoing method ofmaking the heat or cold exchanging element, from the bending or coilinghelically, or otherwise, of the flat ribbon II flatways about the tubeor body portion I0, until the completion of the product with the rib orfin standing upon its own foot I2 and at the desired angle from the tubeor body portion I0, may all be performed by hand, or by metal spinningor by a number of existing mechanisms, with or without substantialmodification of such mechanisms, as may be understood by those skilledin this art after becoming familiar with our method as well as ourprovided apparatus.

Our methodiand the apparatus which we have provided for practicing thesame are related and dependent inventions. The apparatus portion of ourinvention substantially demonstrates the utility as well as practicalvalue of the method portion of our invention. The apparatus portion ofour invention furthermore materially contributes to the understanding ofour invention by those skilled in this art, more particularly withrespect to the practice of the method portion of method.

In connection with the apparatus devised by us for the most economical,rapid and emcient practice of our method which we have thus far ofribbon II.

said tube or body portion II). A roller I5 having a central bearingportion I6 revoluble in bearing member I1 is attached in any desirablemanner to the usual cross-slide He, or other member, of the lathe orlike tool which bears the usual tool post and in such relation to tubeor body portion III that the peripheral portion II of roller I5 engagesthe narrow edge I2 of the ribbon of metal H so as to hold such portionof such ribbon firmly against the outer surface oi the tube or bodyportion I0, with the adjacent face of shoulder IQ'of roller I5 bearingagainst the outer lateral edge of portion I2 of ribbon II.

The portion I8 of roller I5 is provided with a small narrow projectinghead 20. This bead 20 is either continuous or provided with shortinterruptions and extends completely around the peripheral portion I8 ofroller I5, and it projects therefrom at a point intermediate the widthof said portion I 8 so as to engage a portion intermediate the width ofportion I2 of ribbon II. In operation. the bead forms a' shallowindentation 2| in the outer surface ofiportion I2 In thus formingindentation. adjacent metal of said portion I2 is forced inwardly andbelow the adjacent exterior surface of the tube or body portion I0, thusforming an indentation 22 in the exterior surface of tube or bodyportion III. This secures portion l2 of ribbon II firmly to the tube orbody portion I0 throughout the extent that a ribbon Il may be formed orcoiled about the tube or body portion Ill. When the ribbon I l isarranged in a straight line upon or about the body portion ill, the axisof roller I5 is disposed at a right angleto said straight line; but whenribbon II is, for instance, disposed at an angle to a direction of thebody portion III, for instance helically, the axisof roller I5 isdisposed at a right angle to such angle, or to the course of the helix.A structure admitting of such variable mounting of roller I! isindicated in Fig. 6 in which the bearing member II comprises the outwardend of the upper bend and of a standard I'Ia having a circular base nobearing in a recess in the upper surface of the cross-slide He, or likemember, of a lathe or similar tool which usually bears a tool post. Saidbase III) is provided with a slot IIc through which, and a portion ofcross-slide IIe, extends a bolt IId for maintaining base I lb andstandard I'Ia with roller IS. in any of their desired angular positions.To counteract the lateral deflection of tube or body portion I 0 due tothe thrust thereon of roller I5 one or more rollers 23 having bearingsin member 23a a'djustably secured to projection 24 of, or attached to,crossslide He, by bolt 24a, facilitates the engagement of rollerorrollers 23 with the tube or body portion II) at a point or pointsopposite to and aligned with the point of engagement therewith of rollerI5. When the bead 20 is continuous,- the depressions 2| and 22 arecontinuous, but

when the bead 20 is interrupted the depressions 2I and 22 arecorrespondingly interrupted. In the latter case we have found that suchbrief interruptions do not impair the securement of portion I2 of ribbonII to the tube or body portion III.

A bar 25 extending preferablyparallel with, but spaced apart from, anadjacent surface of the tube or body portion I0, is also mounted uponand supported by the cross-slide He, or other portion, of the lathe orlike tool which usually bears the tool post. Removably secured to bar 25by bolts 260 or otherwise, are a plurality of separate tool shanks 21which extend from bar 25 toward the tube or body portion I8. Upon thebelow the horizontal, such mostadjacent portion 28 extending inward andslightly downward from shank 21 and toward the roller I5, the edgeportion-thereof nearest the tube or body portion I0 being provided witha beveled edge 29, Fig. 3,'to provide clearance between such edge 29 andthe adjacent surface of tube or body portion III to accommodate thecoiled portion of the ribbon II. The angle of each succeeding portion 28of each succeeding shank 21 is, progressively increased until theportion 28 of the shank 21 most remote from roller I5 is at such anglethat the surface of its portion 28 nearest to the roller I5 is atsubstantially a right angle, or such other angle relative to the tube orbody portion I8 that the finished rib formed from ribbon II is desired.to stand relative to the tube or body portion III.

The operation of the mechanism thus far described will now be explainedwith relation to the helical coiling of the ribbon II about the tube orbody portion II) which latter is inserted in the lathe adjacent the tipends of portions 28 and between rollers I5 and 23 and mounted betweencenters 58, 52 and mounted in any usual manner to be rotated by thelathe. The cross slide He is moved, with the parts Ho, 24, 25 and theirattachments mounted thereon, adjacent center 5|. As is usual with lathework which may be performed only within an area between centers 58, 52in which the required tools will not be interfered with, the ribbon IImay be wound or helically coiled upon tube Ill within such area. In thiscase such area commences under roller I5 when the cross slide He is insaid moved position and may continue toward center 52 and terminate atsuch point on tube III that roller I5 and portions 28 and theirassociated parts may have clearance between center 52 and the terminalcoil of ribbon I0 after the last of portions 28 have acted upon theterminal portion of the coiled ribbon lIa which the uncoiled ribbon issevered from the coiled portion thereof. The length of the tube Inemployed being such as willsafford the required length of the coils ofribbon II thereon. as well as said clearance spaces at both ends of thetube III. The angularity required for such desired helical coiling isfixed by the adjustment and securement of base I") to I16. This likewisecorrespondingly adjusts the guide for ribbon II in its approach toroller I5. Said guide may be conveniently formed of a projecting arm I1fextending from bearing'member I1 and having a slot I19 in its outer endthrough which the ribbon I I loosely extends toward the roller I5.Ribbon II is led from a convenient roll or other source of supplyloosely through slot Hg and thence without longitudinal or other stressto the roller I5. The loose end of ribbon II is placed between tube orbody portion I8 and surface I8 of roller I5 with its adjacent edgeagainst shoulder I9 of roller I5, the remaining portion of ribbon IIresting upon a portion of the outer surface of hollow conical portion 28of the most adjacent shank 21. The rotation of tube or body portion I8between the centers of the lathe or like tool will cause the helicalcoils about tube or body portion III of the ribbon I I when the end ofribbon I I is forced between the tube and roller I5 in the positionbefore stated. It will be understood by those skilled in the art thatthe lathe or like tool will also be set to longitudinally move thecross-slide I1e relative to the rotating tube or body portion I 0 at therate corresponding to the required angle at which the ribbon I I is tobe helically coiled about the tube or body portion II). In such helicalcoiling of the ribbon II about the tube III its portion I2 will befirmly and continuously secured to the tube or body portion II] by theinterlocking metal comprising the depression 22, as well as further bythe fact that the ribbon I I extends repeatedly around the tube or bodyII). This securement of the portion I2 of ribbon II also forms a slightbend in the ribbon II at-a point between its portions II and I2 due tothe securing pressure of roller I5 upon portion I2 of ribbon II whilethe portion II thereof is resting upon the outward conical surface ofportion 28 of shank 21 nearest to roller I5. In the progression of thiscoiling of ribbon II about the tube or body portion III the engagementof the inner surface of ribbon II with the exterior surface of saidhollow conical segmental portions 28, as the end of the original ribbonII starts to be so coiled, tends to slightly outwardly bend as well asstretch the coiled portion of ribbon II by and throughout the extent theangularity of the engagement of the initial hollow conical segmentalportions 28 of shanks 21. This engagement also exerts a spinning actionupon the coiled portion of the ribbon II which progressively bends aswell as stretches the metal of ribbon II, and which stretching occursmost at the unsecured edge of ribbon II and least or practically nothingat the point between the portions III and II of the ribbon. As theribbon continues its coiling beyond the point where it engages with theinitial segmental portion of the hollow cone 28 of shank 21 nearestroller I5, the end of the coiled ribbon II extends about the tube orbody III, under and free from the inner surface of the before mentionedportion 28, thence again completely around the tube or body portion I8until the same engages the exterior surface of a similar portion of thenext succeeding hollow cone 28 having a similar shank 21 but slightlymore inclined than the first portion 28. This second portion 28 furtherbends and stretches the coiled ribbon progressively at a further anglefrom the tube or body portion ID. From this pointonward the coiledportion of ribbon II at every alternate coil is engaged by a furtherseparate portion 28, each of progressively greater inclination, and eachseparately supported by its own shank 21, and each further progressivelyoutwardly bending and stretching the wound ribbon III, by reason of saidportions 28 being each outwardly inclined on their outer surfaces at aprogressively increasing angle, until the coiled ribbon II is finallyfinished and projects from the tube or body portion III at the desiredangle, which is usually a right angle. The outward bending andstretching of the ribbon II, while it is being formed aboutthe tube orbody portion In by the separate slight progressive changes due to thesuccessive and progressive action on such ribbon by each of thesuccessively spaced and positioned portions 28 of,fdifierentangularities ribbon IIfthe outer edge of the formed ribbon of metalbeing the thinnestQiand the intermediate of' theformed ribbonbeingsubstantially progressively thicker at intermediate pointsthroughout the width, and thickest (being of the normal thickness ofribbon II at the point of juncture of the formed ribbon I I with itssubstantially right angled foot I2. This bending and stretching of theouter portion, as distinguished from portion I2, of the ribbon II whileit is being formed is caused by the frictional engagement of theportions" progressively'with the same under surface of the ribbon I I,while being formed. The temperature resulting from such engagement,coincident with the longitudinal stress created in the ribbon :I I whilebeing bent outwardly concurrently contribute to the stretching action ofthe metal; The longitudinal stress, and therefore-the stretching, isgreater at the outer edge of the ribbon IIwhile being formed,

; II to be employed than was heretofore possible,

which greatly increased the lightness, cost, number of coils of ribbonII per unit of length, in-

' creased the heat or cold exchanging rate and consequently reduced thesize, space and weight requirements for such exchange unit to attain agiven exchange capacity;

(b) Such wider, thinner coils of ribbon II in greater number-per unit oflength of the tube or body portion II'I, which would otherwise be lessstable and more'readily deformed and laterally bent together or ofunequal spacing apart are by our method and apparatus provided with asubstantial longitudinal stress which is uni-directional about andexerts no lateral deflecting influence upon the tube or body portion Innotwithstanding the magnitude of such longitudinal stress; thatvtheribbon II is devoid of such stress as it approaches the point of beingwound about the tube'or body portion III; that said stressprogressivelystretches the metal of the ribbon II while being formed about the tubeor bodyportion I and such stress continues in the finished product to adegree less than that required to further stretch the metal of thefinished formed ribbon I I. Suchpermanent stress of the metal i of thefinished formed ribbon II gives greater stability and resistance todeformation-and lateral bending of each of the finished formed portionsof the ribbon II, as well 'as' increases the rate of conductivity ofheat or cold of the metal of such formed and stressed portions of ribbonI I due not only to the cold working of theribbon II in forming thesame, but to the stretching as well as the permanent stress in theformed ribbon II and (c) The greater rapidityof the production of thefinished heat exchanger element in accordance with our inventionincreases thecheapness of the same without detracting from butincreasing the quality, efllciency, and durability of the finishedproduct; the freedom from complex-, ity of required production mechanismand the direction of roller I5.

greater useful life of the required production mechanism, due to theabsence of the substantial longitudinal stress upon the ribbon II at thepoint where it commences to be wound about the tube or body portion III;the pleasing uniform high polished appearance of the finished product;the ability to employ a very wide much thinner ribbon II than waspossible to heretofore use without precoiling edgewise to a diameterlarger than the tube or body portion I 0 before coiling the same uponeach tube or body portion; the requirement that the tube or body portionIII may have a thin wall no more than necessary to resist the pressureand corrosion or other deteriorating action thereon in normaluse becausesuch Wall requires no grooving or other working, which may lessenitsresistance, requisite to the winding and securing of the ribbonthereabout, but instead thereof the ribbon II is coiled about the virginunworked wall of the tube or body portion I0 andthe strength andresistance of the wall of the tube or body portion I0 is increased bythe flat winding thereabout of the foot I2 under no initial longitudinalstress but whose bent side is subjected to inward and/or longitudinalstress resulting from the bending and stretching of the metal of theribbon II extending outwardly from such side of the foot I2, as well asby the continuous or slightly interrupted row comprising thedepression2I in the foot I2 resulting in the slight depression 22 in the outerwall of the tube or body portion II) with metal of foot I2 interlockedin such depression 22, which depression and the cold working of themetal resulting in their formation, tend substantially to reinforce thestrength and resistance of the substantially thinner wall of the tube orbody portion Ill.

' One of the bending and stretching portions 28 acting upon ribbon IIwhile it is beingcoiled, bent and stretched about the tube or bodyportion I 0 is illustrated in Fig. 5 which shows an end elevation viewthereof looking toward it from the Instead of the portions 28, ordinaryspinning tools or, rods or sticks may be employed to progressively bendand stretch the ribbon II about the tube or body portion Ill.

It will be'noted from Fig. 3 that in the form of the apparatus thereindisclosed the forming-bybending-and-stretching portions 28 engage thewound ribbon I! at but one point in at least every other coil of theribbon II about the tube orbody'portion III. This afiords a substantialarea of the ribbon II to transmit the heat engendered by auch coldworking operations as said bending and stretching, tothe metal of thetube or body portion ID by conductivity through the metal of the ribbonII as well as very large surface areas of the metalof ribbon II exposedto the atmosphere throughout points thereof which are contacted bysaidportions 28, and which conduction to the atmosphere of such surplus heatof the ribbon I I in its successive forming stages is very substantialand results in a very eflicient, cheap, durable and highly finishedproduct being very rapidly made from the metal comprising the ribbon 'IIwhich may be most advantageous for the employment 'of.the apparatusshownin Fig. 3. Such heat exchange to the atmosphere throughout the areaof ribbon II engaged by successive portions 28 is very substantial forthe further reason that the rotation of tube orbody portion I0 with thewound portion of the ribbon is very rapid and this, together with theprogressive outward bending and tions.

stretching of the metal of ribbon ll creates a substantially increasedcirculation of air around and between the coils of ribbon ll.

Any number of bars 25 supported by cross-slide He may be employed eachwith its row of shanks 21, with their respective portions 28 atdiiferent radial points about the tube or body portion Ill. Fig. 4illustrates such an arrangement in which three bars 25 are employed eachwith attachment similar to those shown and described relative to Fig. 3,each bar 25 being substantially equally spaced about the tube or bodyportion III. In such arrangement the segmental hollow conical portion 28of each shank '21 are of such segmental dimensions that ample space isafforded between the adjacent portions 28 to not only enable theirinsertion and removal, but also to afford a substantial area of ribbonll exposed to the atmosphere and the afi'ordance of substantial heatconductivity from such exposed portions of ribbon H to the atmosphere.

In Fig. 7 is shown a diagrammatic view of a lathe or other tool in whichthe tube or body portion I is mounted between the conical centers 50 oftail-stock i and 52 of head-stock 53. The conical center 52 oihead-stock 53 being rotated by power pulley or motor 54, whichcorrespondingly drives a pulley 55 belted by belt 56 to pulley 51 upon ashaft 58 mounted in bearings 59 on base plate 60, said shaft 58 beingprovided with screw threads 6| engaging a suitable nut mounted upon thecross-slide Me for imparting longitudinalmotion to said slide lle alongbase plate 60 at the rate required to obtain the desired pitch of thehelical coils of ribbon ll about the tube or body portion Ill. To varysuch rate any one of different sized pulleys 55 or equivalent means maybe employed. In conventional view, Fig. 7, the details indicated in Fig.6 are not disclosed for clearness.

To increase the rate of conductivity of the surplus working heat fromthe portions of the ribbon being bent and stretched and from theportions 28 which perform such functions, each shank 21 may be providedwith a longitudinal opening I0 opening to the atmosphere at its endadjacent portion 28 and having its upper end connected to a pipe 12. Airor other fluid under any desired pressure may be passed through pipe 12and opening to and around adjacent surfaces of the ribbon H and portions28 to further increase the rate of heat conductivity occasioned by thecold working of the portions of the ribbon H formed about the tube orbody portion It. The rate of such heat transfer may be controlled byvarying the pressure of the fluid conveyed to each opening 10.

Our invention in each of its related and dependent aspects of method andof apparatus will be readily understood and usable by those skilled inthis art from the foregoing speciflca- This invention may be made andused by or for the Government of the- United States of America forgovernmental purposes without the payment of any royalty thereon ortherefor.

Having now so fully described our invention that others may therefrom beenabled to prac-.

tice, construct and usethe same, what we claim is: I

l. The method of making a heat exchange device including a heat exchangeelement provided with a heat exchange fin secured thereto, comprisingthe steps of securing a portion of a metal strip to a heat exchangeelement to form at least one convolution thereabout and thenprogressively bending the unsecured portion of the strip outwardly ofthe heat exchange element and angularly with respect to its securedportion to directly form by the bending operation a heat exchange fincircumferentially secured to a heat exchange element.

2. The method of making a heat exchange device including a heat exchangeelement provided with a helical heat exchange fin secured thereto,comprising the steps of helically securing a portion of a metal strip toa heat exchange element and then progressively bending the unsecuredportion of the strip outwardly of the heat exchange element andangularly with respect to its secured portion to directly form by thebending operation a helical heat exchange fin secured to a heat exchangeelement.

3. The method of making a heat exchange device including a heat exchangeelement provided with a helical heat exchange fin secured thereto,comprising the steps of helically securing a portion of a metal strip toa heat exchange element with adjacent convolutions of the unsecuredportion of the strip in overlapping relation and then progressivelybending the unsecured portion of the strip outwardly of the heatexchange element and angularly with respect to its secured portion todirectly form by the bending operation a helical heat exchange finsecured to a heat exchange element.

4. The method of making a heat exchange .device including a heatexchange element provided with a' helical heat exchange fin securedthereto, comprising the steps of helically securing a portion of a metalstrip to a heat exchange element with adjacent convolutions of theunsecured portion of the strip in overlapping relation, thenprogressively bending the unsecured portion of the strip outwardly ofthe heat exchange eleso v ment and angularly with respect to its securedment and means for progressively bending theunsecured portion of thestrip outwardly of the heat'exchange element and angularly with respectto its secured portion to directly form by the bending operation thehelical heat exchange fin, said last mentioned means including aplurality of spaced members of varying and progressive angulation withrespect to the element tobe finned and arranged lengthwise thereof.

6. An apparatus for making a heat exchange device including a heatexchange element provided with a helical heat exchange fin securedthereto, comprising means for helically securing a portion of a metalstrip to a heat exchange element and means for progressively bending theunsecured portion of the strip outwardly of the heat exchange elementand angularly with respect to its secured portion to directly form bythe bending operation the helical heat exchange fin, said last mentionedmeans including a row' of spaced overlapping members having a varyingand progressive angulation with respect to the element to be finned andarranged lengthwise thereof.

7. An apparatus for making a heat exchange device including a heatexchange element provided with a helical heat exchange fin securedthereto, comprising means for helically securing a portion of ametal-strip to a heat exchange ale- 5 ment and means for progressivelybending the unsecured portion ofthe strip outwardly of the heat exchangeelement and angularlywith respect to its secured portion to directlyform by the bending operation the helical heat exchange fln,

tinned and arranged lengthwise thereof, at least one of said membersbeing apertured for the ln- 5 troduction of a cooling fluid.

ALFRED J. BERG. JOHN o. HUSE.

